a8735 Allegro MicroSystems, Inc., a8735 Datasheet - Page 14

• Manufacturer Part Number: a8735
• Description: Ultra Small Mobile Phone Xenon Photoflash Capacitor Charger With Igbt Driver
• Manufacturer: Allegro MicroSystems, Inc.

A8735
Layout Guidelines
Key to a good layout for the photoflash capacitor charger circuit
is to keep the parasitics minimized on the power switch loop
(transformer primary side) and the rectifier loop (secondary side).
Use short, thick traces for connections to the transformer primary
and SW pin. It is important that the ¯ D ¯ ¯ ¯ O ¯ ¯¯ N ¯ ¯ E ¯ signal trace and other
signal traces be routed away from the transformer and other
switching traces, in order to minimize noise pickup. In addition,
high voltage isolation rules must be followed carefully to avoid
breakdown failure of the circuit board.
Recommended Components
C1, Input Capacitor
C2
C
Capacitor
D1, Output Diode
T1, Transformer
OUT
Component
, Photoflash
10 μF, ±10%, 6.3 V, X5R ceramic
capacitor (0805)
0.1 μF, 6.3 V X5R ceramic capacitor
100 μF / 330 V
2 x 250 V, 225 mA, 5 pF
L
6.5 × 8 × 4 mm
L
4.6 × 4.6 × 2.4 mm
PRIMARY
PRIMARY
= 12.8 μH, N= 10.25,
= 7.8 μH, N= 9.9,
Rating
Ultra Small Mobile Phone Xenon Photoflash
Capacitor Charger with IGBT Driver
Avoid placing any ground plane area underneath the transformer
secondary and diode, to minimize parasitic capacitance.
For low threshold logic (<1.2 V) add 1 nF capacitors across the
CHARGE and TRIGGER pins to GND to avoid malfunction due
to noise.
Connect the EE package PAD to the ground pad for better ther-
mal performance. Use ground planes on the top and bottom layers
below the IC and connect them through multiple thermal vias.
Refer to the figures on page 18 for recommended layout.
JMK212BJ106K
EPH-31ELL101B131S Chemi-Con
BAV23S
T-16-024A
MTF-S2
Part Number
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Taiyo Yuden
Philips Semiconductor,
Fairchild Semiconductor
Tokyo Coil Electric
Union
Source
14